A Problem in My iPhone’s Earpiece

I guess I've got this problem on my mobile phone around six months back. Whenever somebody calls or even if I myself attempt to call someone I can hardly hear the other side. When I try to shift it to its speaker or have the earphones plugged in that's the only time I could clearly hear the person I am talking with. That's when I realized I've got a problem in my iPhone's earpiece. I have tried to look for iPhone technicians lately but the problem was they don't have the necessary parts just in case they need to replace something. I probably need to have it checked in an Apple store instead. :(